Acting attorney general is a critic of the Mueller investigation

Acting Attorney General Matthew Whitaker — the Department of Justice chief of staff President Trump appointed to lead the department after Jeff Sessions' resignation — is a critic of Robert Mueller's Russia investigation who wrote in a CNN op-ed last year that the investigation was "going too far."

Why it matters: The Justice Department oversees the Mueller investigation. A DOJ official told the Washington Post that Whitaker will assume authority over the probe, which had been run by Deputy Attorney General Rod J. Rosenstein.

Traditionally, the Senate-confirmed deputy attorney general — in this case, Rosenstein — would step in as acting attorney general in the event of a top vacancy. Trump has instead chosen his own pick, which is likely to raise questions about whether the White House wants Whitaker to take a more hard-line stance on the investigation.

The background: Whitaker was formerly a U.S. attorney for the Southern District of Iowa and ran for Senate in Iowa in 2014, but lost in a primary to Joni Ernst. He played college football at the University of Iowa, where he was a tight end and went to the Rose Bowl.

Whitaker is considered a Trump loyalist, and "has served as what one White House aide called a 'balm' on the relationship between the president and the Justice Department," according to the New York Times' Katie Benner and Maggie Haberman.

White House chief of staff John Kelly has called Whitaker the White House's " eyes and ears" at DOJ, per the Times.

He's been floated before as a replacement for Rosenstein and White House counsel Don McGahn.

What to watch: Senate Minority Leader Chuck Schumer has already called for Whitaker's recusal from the Mueller probe. We're likely to see more of this from House Democrats, who now have subpoena power and are expected to launch a slew of investigations of their own into Trump's connections to Russia.